Therapeutic antibodies are being used with increasing frequency and for expanding indications. For example, therapeutic antibodies are used to treat cancer by stimulating anti-tumor immune responses. In another example, therapeutic antibodies are used to treat autoimmune diseases by inhibiting immune responses to self-antigens.
Generally, antibody therapeutics are engineered to bind specifically to antigens (either foreign or self), often with modifications to their Fab regions that increase antibody affinity or avidity. Full-length antibodies include the Fc region that, when bound by Fc receptors on immune cells, triggers a range of effector functions (e.g., pro-inflammatory or anti-inflammatory responses), which contribute significantly to the mechanisms of action of such therapeutics.
The amino acid sequence of human antibody Fc regions is unchanged among all antibodies produced in the body within a given antibody subtype. Thus, while the Fab region provides variability for binding to different antigens, the Fc region provides a constant structure for recognition by Fc receptors.
A variety of human Fc receptor subtypes have been identified on cell surfaces, each binding antibodies through their Fc regions and triggering (or suppressing) particular immune responses depending on the identity of the cell expressing the Fc receptor and the subtype of the Fc receptor. The family of human Fc receptors includes both activating and inhibitory receptors that either induce or negatively modulate effector functions, respectively.
A substantial amount of research has been conducted with the aim of producing antibodies exhibiting selective binding to either activating or inhibitory Fc receptors. This work has revealed that IgG1 antibodies typically used as therapeutics contain a single glycan (carbohydrate moiety) per chain linked to the asparagine residue at position 297 (Asn297) (Radaev et al., (2001) J. Biol. Chem. 276:16478-16483). The presence of this glycan is critical for antibody binding to all Fc receptor subtypes and variations in its chemical composition can modulate Fc receptor binding affinities. Somewhat surprisingly, the majority of antibody/Fc receptor binding interfaces are composed of intermolecular contacts between amino acid residues from each of the two proteins, and do not involve atoms from the glycan linked to Asn297. Therefore, additional research has been conducted to determine whether modifications to the particular amino acids of antibodies found within this interface will result in the development of antibodies having predictable affinities for selected Fc receptor subtypes (Shields et al., (2001) J. Biol. Chem. 276:6591; Lazar et al., (2006) Proc. Natl. Acad. Sci. 103:4005-10; Richards et al., (2008) Mol. Cancer Ther. 7:2517-27; Chu et al., (2008) Mol. Immunol. 45:3926-33).
It can thus be seen that antibodies engineered to selectively bind either activating or inhibitory Fc receptors will likely exhibit improved therapeutic efficacy versus antibodies with wild-type Fc regions. For example, antibodies engineered to increase binding to activating Fc receptors and/or decrease binding to inhibitory Fc receptors could intensify effector functions that aid in the removal of malignant cells and, thus, function as improved versions of anti-cancer therapeutic antibodies. The present invention is directed to the development of such antibodies, as well as other important goals.